1. Field of the Invention
The present invention relates to an activated carbon fiber structure excellent in processability, durability, adsorptive and desorptive characteristics, etc., and to a process for producing the same. More particularly, the present invention relates to an activated carbon fiber structure well adapted for use as an adsorbent, a deodorizer, a filter, etc., and to a process for producing the same.
2. Prior Art
Activated carbon fibers are produced by treating a variety of respective carbon fibers or precursor fibers of carbon fibers with steam, carbon dioxide or the like to activate the same. However, no carbon fibers which are satisfactory in overall performance, including processability, durability, etc., have so far been materialized.
For example, activated carbon fibers of phenolic resin type have a large specific surface area and can be relatively arbitrarily controlled in pore size. Therefore, they are characterized by a wide range of adsorbate substances ranging from low molecular weight ones to high molecular weight ones as well as a large amount of adsorption. However, phenolic resin fibers as the precursor fibers of these activated carbon fibers have a defect of poor processability during the course of forming the same into a fiber structure because of their low tensile strengths, despite their large elongations.
In order to obviate this defect, the activated carbon fibers or the precursor fibers thereof are reinforced with a high-strength fiber. However, this quite often entails deteriorated overall adsorption efficiency and reduced heat resistance of the reinforced structure.
Furthermore, since phenolic resin fibers are large in shrinkage during the course of heat treatment thereof for activation (hereinafter referred to as "activation treatment"), there arises a problem that a large morphological change occurs between before and after activation treatment.
On the other hand, activated carbon fibers of pitch type are substantially comparable in adsorptive performance to the activated carbon fibers of phenolic resin type, and have been high in tensile strength and modulus of elasticity before activation thereof. Nevertheless, the activated carbon fibers of pitch type tend to be brittle because of their small elongations. This presents a problem of poor handleability of fiber during the course of shaping the fiber into a structure.
Unlike common organic fibers, carbon fibers of pitch type are relatively free from twisting, bending and crimping, and substantially circular in cross section, with the result that they have a characteristic liability to undergo interfiber adhesion. This favorably increases the utilization of fiber strength in the case where the carbon fibers are used as reinforcing fibers, but presents a problem that, when the carbon fibers are used as adsorbents, fluid migration is hindered to keep an adsorbate component from diffusing through interfiber spaces because the fibers are liable to undergo interfiber adhesion. Furthermore, the carbon fibers of pitch type involve the difficulty in effective needling because of their liability to interfiber exfoliation, thereby presenting a problem that a difficulty is encountered in manufacturing therefrom mats and the like with high bulk density.
An object of the present invention is to provide an activated carbon fiber excellent in overall performance, including processability, adsorptive and desorptive characteristics, etc., and a structure constituted thereof.
Another object of the present invention is to provide a solution to the problems ensuing from the low strengths and large shrinkages of the conventional organic fibers such as phenolic resin fibers.
A further object of the present invention is to provide such an improvement as to overcome the small elongations and poor processabilities as well as problematicaIly excessive interfiber adhesion or exfoliation of the conventional activated carbon fibers of pitch type.